1. Field of the Invention
The present invention relates to a three-point seat belt device, and more particularly to a three-point seat belt device having a webbing with its one end movable by a swingable lever.
2. Description of the Prior Art
There is known a three-point seat belt device or a combination lap and shoulder belt device having a single webbing or use in automobiles. In such a prior seat belt device, the webbing is unreeled from a retractor mounted on a side wall of an automobile compartment and threaded through a through anchor attached to an inner surface of a center pillar, the webbing having an end fixed to an automobile body side seal disposed laterally of a passenger's seat. The webbing carries thereon a tongue plate at a position between the through anchor and the webbing end. The tongue plate is engageable with a buckle located laterally of the seat near the center of the automobile body for holding the webbing against the shoulder and waist of a passenger sitting on the seat. For allowing the passenger to fasten the seat belt with ease, it is necessary to set the end of the webbing in such a position that a portion of the webbing in the vicinity of the tongue plate should be located in front of the back of the seat. However, there was a dilemma that setting of webbing in such position causes the interference of the webbing with the passenger while his getting on or off the seat.
To solve such a dilemma, Japanese Laid-Open Utility Model Publication No. 121020/1977 has proposed a seat belt device, wherein a lever is mounted on a side of the seat facing the door swingably in the back-and-forth direction, and the end of the webbing is secured to the lever. The lever is turned foward when the seat belt is to be fastened, and is turned backward when the passenger is to get on or off the seat. This seat belt device has been effective in improving the ease with which the seat belt is fastened and the passenger gets on and off the seat. However, there was a problem with the disclosed seat belt device that a large drive force is required to turn the lever back and forth. The problem will hereinafter be described in detail with reference to FIG. 12 of the accompanying drawings.
Designated in FIG. 12 at D is a position where a through anchor is attached to an automobile body, and E a position where the swingable lever is coupled to the automobile body. An arc ABC indicates a path of movement of the movable end of the lever to which the end of the webbing is secured. Also denoted at A and C are rear and front limit positions of the range in which the movable end of the lever is movable, and B is a point where a straight line DE intersects the arc ABC. When the lever is angularly moved forward from the rear limit, the upper end of the lever is moved from the point A to the point B at the first stage. On such angular movement of the lever, an initial distance AD between the through anchor and the upper end of the lever is reduced to a distance BD, and hence the webbing is wound into the retractor by the length equal to the difference between distances AD and BD. Continued forward angular movement of the lever brings the upper end thereof to the point C, during which the distance between the through anchor and the upper end of the lever is increased by the difference between CD and BD. Accordingly, the corresponding length of the webbing should be pulled out of the retractor against the winding force of the retractor. The lever therefore requires a large drive force for the latter half of the forward angular movement. Similarly, the lever requires a large drive force for the latter half of the rearward angular movement thereof.
If the lever is angularly moved back and forth by a motor, the motor should have a large capacity. If the lever is turned back and forth by a control wire or the like which are coupled with a door, the opening and closing of the door should be rendered relatively heavy.
Another drawback is that the lever is subject to the winding force from the retractor at all times so that it is difficult to move the lever accurately into and hold it stably at the front and rear limit positions.